Ions control the function of heart muscle. In particular, sodium, potassium and calcium are vital not only in maintaining normal electric activity but also contractile behavior. This project involves a study of all membrane systems and proteins involved in the cellular control and modulation of these ions. These include cell membrane Na ion, K ion-ATPase, a transport enzyme; the sarcoplasmic reticulum which is responsible for muscle relaxation; mitochondria which provide a usable form of energy and also sequester ions and troponin; a calcium receptor protein.